The present invention relates to a magnetic induction system for wirelessly transmitting power and/or data through a barrier. More particularly, the invention relates to a method for mechanically modifying the barrier to improve the flow of magnetic flux from the magnetic field transmitter to the magnetic field receiver to thereby increase the power transfer efficiency of the system.
Systems which employ magnetic induction to wirelessly transmit power and data signals through barriers are known in the art. Referring to FIG. 1, such induction power and data transfer systems commonly include a magnetic field transmitter 10 which is positioned on one side of a barrier 12 and a magnetic field receiver 14 which is positioned on the opposite side of the barrier. The magnetic field transmitter 10 typically includes a transmitter coil 16 which is wound around a transmitter core 18 and the magnetic field receiver 14 usually includes a receiver coil 20 which is wound around a receiver core 22. The transmitter 10 is connected to a signal generator 24 which when activated generates a time varying current that flows through the transmitter coil 16. The flow of current through the transmitter coil 16 generates a time varying magnetic field which in theory flows through the barrier 12 to the receiver 14. At the receiver 14, the time varying magnetic field flows through the receiver core 22 and causes a current to flow through the receiver coil 20 which may then be used to power a device 26 that is connected to the receiver coil.
Although induction data transfer systems work reasonably well with barriers made of many types of materials, induction power transfer systems usually work satisfactorily only with barriers made of materials having relatively low magnetic permeabilities. The reason for this can be explained by reference to FIGS. 2 and 3, which are representations of the induction power transfer system of FIG. 1 showing the paths the magnetic field lines generated by the transmitter 10 follow when the barrier 12 is made of a material having a relative magnetic permeability of around 10 and a material having a relative magnetic permeability of around 100, respectively. As shown in FIG. 2, when the relative magnetic permeability of the barrier 12 is around 10, a substantial portion of the magnetic field lines generated by the transmitter 10 flow through the barrier and into the receiver core 22. As shown in FIG. 3 on the other hand, when the relative magnetic permeability of the barrier 12 is around 100, relatively few of the magnetic field lines flow through the barrier and into the receiver core 22. Instead, most of the magnetic field lines generated by the transmitter 10 “short” through the barrier 12 and return to the transmitter core 18 before reaching the receiver core 22.
The power transfer efficiency of an induction power transfer system is directly proportional to the amount of the magnetic flux generated by the transmitter which flows through the receiver core. The amount of magnetic flux in the receiver core in turn is proportional to the number of magnetic field lines which pass through the transverse cross section of the receiver core. Comparing FIG. 2 with FIG. 3, therefore, one can see that the amount of magnetic flux in the receiver core 22 when the relative magnetic permeability of the barrier 12 is around 10 is significantly greater than the amount of magnetic flux in the receiver core 22 when the relative magnetic permeability of the barrier is around 100. Therefore, the power transfer efficiency of the induction power transfer system will be greater when the barrier 12 is made of a material having a relatively low magnetic permeability.
However, the power transfer efficiency does not continue to increase as the magnetic permeability of the barrier decreases. FIG. 4 is a representation of the induction power transfer system of FIG. 1 showing the paths the magnetic field lines generated by the transmitter 10 follow when the barrier 12 is made of a material having a relative magnetic permeability of around 1. Comparing FIGS. 2 and 4, one can see that when the barrier 12 is made of a material having a relative magnetic permeability of around 1, a smaller proportion of the magnetic flux generated by the transmitter 10 is coupled into the receiver core 22 than in the case when the barrier is made of a material having a relative magnetic permeability of around 10. Therefore, the power transfer efficiency of the system in which the barrier comprises a relative magnetic permeability of around 1 is less than the power transfer efficiency of the system in which the barrier comprises a relative magnetic permeability of around 10.
However, in many applications in which wireless induction power transfer systems would be beneficial, the barriers are made from materials having relatively high magnetic permeabilities. For example, in the subsea oil and gas production industry, electrically powered devices such as sensors, transmitters and actuators are sometimes positioned inside the production equipment components, such as wellhead housings, christmas tree flow lines and valve actuators, in order to monitor and control the flow of fluids through the components. Although power for these electrically powered devices may be provided by internal batteries or external power supplies, batteries lose charge over time and external power supplies require the drilling of holes through the components to accommodate pass-through connectors, and such holes are undesirable when the pressure integrity of the components must be assured.
Therefore, a wireless induction power transfer system for powering devices positioned inside subsea hydrocarbon production equipment components would be beneficial. However, many of the common materials used to manufacture these components, such as 4130, X65, Super Duplex and 1010 steel, have relative permeabilities near 1000. Consequently, the power transfer efficiencies for an induction power transfer system for use with these components would likely be only a small fraction of a percent. As a result, induction power transfer systems are not practical for use with such components.
In other applications in which wireless induction power transfer systems are currently employed, the power transfer efficiencies are less than ideal because the barriers are made from very low magnetic permeability materials. For example, cordless charging stations employing wireless induction power transfer systems have been developed to recharge a number of portable devices, such as cell phones, personal media players and cameras. However, these devices commonly comprise housings made of very low magnetic permeability materials, such as plastic. As a result, the power transfer efficiency of the charging station is relatively low. Consequently, a relatively long time is required to fully charge the device and the charging efficiency is substantially lowered.